The present invention relates to a pneumatic tire suitable as a studless tire, and more particularly to a pneumatic tire having a good steering stability on dry roads improved while keeping lowering of performances on snow-covered roads to the minimum.
Pneumatic tires suitable for traveling on icy and snow-covered roads, including for example studless tires, usually have in the tread surface a plurality of circumferential grooves extending in a circumferential direction of a tire and a plurality of lateral grooves extending in a direction intersecting with the circumferential grooves to form a plurality of blocks in which a plurality of zigzag sipes are further provided, as known for example from JP-A-11-310013 and JP-A-2005-041393. The performances on snow-covered roads (hereinafter referred to as “on-snow performances”) are secured by a shearing force of snow columns formed in the grooves and an edge effect obtained by edges of the blocks and the sipes.
It is known that it is preferred for the on-snow performances to increase the volume of grooves, thereby enhancing the shearing force of snow columns, and to increase the number of sipes to be formed, thereby enhancing the edge effect.
However, increase of the groove volume and increase of the number of sipes lead to lowering of the block rigidity, thus resulting in deterioration of steering stability on dry roads (hereinafter referred to as “dry steering stability”). The on-the-snow performances and the dry steering stability are performances repugnant to each other and, therefore, it is difficult to simultaneously maintain both performances on high levels.
Accordingly, it is an object of the present invention to provide a pneumatic tire which is suitable for traveling on icy and snow-covered roads and, moreover, the dry steering stability of which is improved with keeping lowering of the on-snow performances to the minimum.
This and other objects of the present invention will become apparent from the description hereinafter.